The present invention relates to a sealing system for a metal gasket and gasket attaching portions thereof. The sealing system may be used for a general type of a gasket, but preferably, the gasket is used for an internal combustion engine as a cylinder head gasket, a manifold gasket and so on, and is especially useful for a thin gasket formed of one or two metal plates.
A gasket for the engine is installed between two engine parts, such as between a cylinder head and a cylinder block, between a cylinder head and a manifold, and so on, for sealing and connecting the engine parts. Since high pressure and temperature are applied to the gasket in the engine, a metal or metal laminate gasket has been used widely. In view of the weight and economy of the gasket, the gasket is made as thin as possible. Thus, the gasket may be formed of one or two metal plates.
In the metal or metal laminate gasket, in order to securely seal around a hole to be sealed, a metal plate is often provided with a bead and/or turning portion around the hole to thereby provide a high surface pressure thereat. A grommet nay be installed around the hole instead of or together with the bead.
The bead formed on the metal plate projects outwardly from the metal plate, and has a curved shape or flat sections with linear corners in a cross section. When the bead is compressed in use, a curved top portion or linear corners of the bead are compressed, so that the bead generally provides a linear contact, not area contact, and provides a high surface pressure in a small area.
In case the bead contacts another plate for forming the gasket, the high surface pressure formed on the bead is relatively widely spread. However, if the bead directly contacts a gasket attaching portion of the engine, the gasket attaching portion receives the high surface pressure directly and causes a trouble, such as forming depression or deformation of the gasket attaching portion.
For example, when the metal laminate gasket is formed, the thickness of the metal plate is 0.2-0.4 mm; the height of the bead is 0.15-0.5 mm; and the width of the bead is 0.3-2.0 mm. When the bead makes a linear contact, the width of the contact is limited to 0.2-0.5 mm. In a single metal plate gasket, the thickness of the metal plate is slightly increased. However, in any cases, when the engine is actuated and stopped, the gasket is heated and cooled repeatedly and cyclically, and the contact area changes gradually. Thus, the sealing ability of the bead is gradually reduced and degraded. Therefore, it is preferable to form a wide sealing area with the area contact, not the linear contact, in the metal gasket.
In U.S. Pat. No. 5,221,097, an engine and a gasket form a sealing system, wherein an annular groove is formed in the engine, and a bead formed in the gasket is disposed in the annular groove. The sealing system of the patent operates as intended, but there is a room to improve the sealing system.
Accordingly, one object of the present invention is to provide a sealing system for a gasket and gasket attaching portions, wherein the gasket can securely seal between the gasket attaching portions with a wide sealing area.
Another object of the invention is to provide a sealing system as stated above, which can be used for a thin metal gasket.
A further object of the invention is to provide a sealing system as stated above, which can be used for a variety of gaskets.
Further objects and advantages of the invention will be apparent from the following description of the invention.